Move list from the view model to the validation rules class

Question

Im using the following example and it the list which should need to do the validation to is currently

inside the validation rules class but now I need to get it from outside and the list can be changed during RT,

how can I send the list from the view model to the validation rules class

 public class PropertVal : ValidationRule
    {
        private readonly List<String>  validValues = new List<String> { "aa", "bb", "cc", "dd" };
        public override ValidationResult Validate(object value, CultureInfo cultureInfo)
        {
            if(value == null)
                return new ValidationResult(false, "The Field are not match");

            string val = value.ToString().Trim();
            bool isValid = !string.IsNullOrEmpty(val) && validValues.Contains(val);
            ValidationResult result = null;
            result = isValid
                         ? new ValidationResult(true, null)
                         : new ValidationResult(false, "The Field are not match");

            return result;
        }
    }

XAML

<TextBox>
    <TextBox.Text>
        <Binding Path="NameOfViewModelPropery" UpdateSourceTrigger="PropertyChanged"
                 >
            <Binding.ValidationRules>
                <local:PropertiesMapValidation ValidatesOnTargetUpdated="True"/>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

Answer 1

I have a solution but it need to be tested: First you can not use directly the property validation in the binding, because it creates a new instance of the class and then you can not add items to the validation list. I create an instance in the resource base in the App.xaml file:

<Application x:Class="WpfApplicationTest.App"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:WpfApplicationTest="clr-namespace:WpfApplicationTest" StartupUri="MainWindow.xaml">
<Application.Resources>
    <WpfApplicationTest:PropertVal x:Key="propertVal" />
</Application.Resources>

In this way you can access it from any part of the application, this is an example in a MainViewModel class that I have created:

public class MainViewModel
{
    public void AddValue()
    {
        var propVal = App.Current.MainWindow.Resources["propertVal"] as PropertVal; 
        if (propVal == null)
            return;
        propVal.AddListItem("Some New Item");
    }
}

But for doing this I need to create public methods in the PropertVal class:

public class PropertVal:ValidationRule
{
    private readonly List<String> validValues = new List<String> { "aa", "bb", "cc", "dd" };
    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        if (value == null)
            return new ValidationResult(false, "The Field are not match");

        string val = value.ToString().Trim();
        bool isValid = !string.IsNullOrEmpty(val) && validValues.Contains(val);
        ValidationResult result = null;
        result = isValid
                     ? new ValidationResult(true, null)
                     : new ValidationResult(false, "The Field are not match");

        return result;
    }

    public void AddListItem(string item)
    {
        //...
    }

    public void RemoveItem(string item)
    {
        //...
    }
}

Then filanlly use it in the xaml code:

<TextBox>
        <TextBox.Text>
            <Binding Path="NameOfViewModelPropery" UpdateSourceTrigger="PropertyChanged">
                <Binding.ValidationRules>
                    <StaticResource ResourceKey="propertVal"/>
                </Binding.ValidationRules>
            </Binding>
        </TextBox.Text>
    </TextBox>

Hope it helps. This is an idea I have not fully tested, but hope helps...

Answer 2

For that you need to bind your List from ViewModel to your validation class and Unfortunatly You can't add bindings to properties on classes that derive from ValidationRule in the normal way. This is because validation rules don't sit in an inheritance context and don't derive from DependencyObject.

Similar Result can be achieved by using DataSource Techinique as described in this blog

I have used this technique and worked perfectly fine.